1. Field of the Invention
The present invention relates to a device for selectively controlling the connection of devices to a telephone line.
2. Brief Description of the Prior Art
In recent years, digital communication devices such as MODEM and FAX are often used to share a telephone line with the telephone sets.
Before the telephone call is connected, the telephone user of the receiving and could not differentiate the voice or digital communication source devices. There is no way to automatically guide the telephone call to the expected devices before it is connected. This causes the telephone user to buy an extra phone line for the different digital communication device.
U.S. Pat. No. 5,056,132 to Coleman et al, which was issued on Oct. 8, 1991, teaches a telephone signal switch device to request a code from the caller to identify the incoming communication, the communication is connected to the identified or preselected communication device. This apparatus wastes a call if the identified communication device is telephone hand set but no human answer is available.
U.S. Pat. No. 5,070,523 to Hafer et al, which was issued on Dec. 3, 1991, allows the calling station to select which hand set or device is to be connected by entering a dual-tone multi-frequency code and plans priority of use of the public telephone line by the connected devices. This apparatus fails to direct data of FAX of calling station if the dual-tone multi-frequency is not entered after the initial call in case the called station sets its first priority of communication to telephone hand set. Since "all ports are physically identical and, disregarding priorities, any combination of telephones and other devices can be plugged into ports in any order", how MODEM/FAX of the distant station determines which dual-tone multi-frequency code is needed in order to guide this apparatus to route the data of MODEM/FAX to the desired port? How data of MODEM/FAX are sent through this apparatus to a MODEM/FAX of a distant station which connects MODEM/FAX to telephone jack directly? Changing the micro processor chip to set the priority to direct the communication to the corresponding ports is not easy for customers who buy the product of this invention.
Some telephone companies offer the Special Ring option to give a second telephone number to share same telephone line with the original telephone number. The audible rings of the second telephone number is different with the original one. When receiving a telephone call, telephone line user can realize which telephone number is called. The telephone line users need to pay for the Special Ring option. And the Special Ring option does not help to route the telephone call to certain desired telephone devices.
Carrier detectors, which are used to detect the existence of the telephone carrier and then of carrier and then of the communication between the caller and receiver, usually come with MODEM chips, and are expensive. Stand alone carrier detectors for the telephone carrier are not easy to get from the industry. Designing one could be more expensive.